If it's prone to randomly stopping, you've probably got link-layer problems... sftp, of course, is slower than ftp, but I've used that with good success.

As for the special USB cable: one of those is available, but not from Nokia. It wouldn't do away with the need for a power adapter, though, because the power adapter that comes with it is 980mA, and USB is maximum of 500 mA. You'd consign yourself to slow charging, and inability to maintain a charge during heavy usage.

Also, ditching USB also ditches USB host-mode (which is another troublesome spot WRT charging over USB), and that's not a tradeoff that seems beneficial. Better perhaps is to get USB-networking to work on all versions of Windows, make that the default usage of USB, and support file transfer (probably via SMB) over that network. But charging still has to be separate to allow host mode to work well.